Fermi Telescope Makes Valuable Use of Gravitational Lens

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A team of international astronomers are using the Fermi Gamma Ray Space Telescope to observe an active galaxy 4.35 billion light years away. Currently orbiting in our solar system, the Fermi is able to observe traveling gamma rays from this far off galaxy by taking advantage of an intermediary gravitational lens, a phenomenon by which the rays are essentially magnified, and thus, made easier to observe. Gravitational lenses occur when gamma rays pass by an object and become distorted and amplified by the object’s gravitational pull. Observations made by this method can shed light on the nature of distant galaxies and the black holes that initially emit the gamma rays themselves.

The Fermi telescope is a space observatory currently in low earth orbit. This observatory is equipped with two main instruments; the Gamma Ray Burst Monitor (GBM) and the Large Area Telescope (LAT). The GBM is used for initially detecting gamma ray bursts over a wide range, and the LAT is used in capturing an image of the traveling rays.

Both of these instruments have allowed scientists to observe light from the center of a far away galaxy cleverly titled B0218+357. B0218+357 is classified as a “blazar” due to its intense emissions and relative unpredictability. This particular galaxy has, at its center, a supermassive black hole (basically a black hole in DK mode) which has a mass of anywhere from a million to a billion times that of our sun. It is from the activity of this huge black hole that the Fermi gains insight into its surrounding galaxy.

As matter is sucked into the black hole, gamma rays are blasted outward and away from the hole in opposite directions, traveling at nearly the speed of light (speed of light = 299,792,458 m/s = pretty fast). In the case of B0218+357, these speedy gamma rays set a course right through our solar system, making them eventually detectable to the Fermi. But the Fermi could not make these observations without the help of another galaxy sitting between it and B0218+357.

In between B0218+357 and the Fermi is a spiral galaxy that is crucial in making the former observable to the latter. Think of this helpful mass of gas as a galactic broker in this whole operation. As the jets of gamma rays pass through this intermediary galaxy, they are magnified to the point where the Fermi can pick them up using the LAT. In addition to amplifying the B0218+357 gamma rays, the intermediary galaxy’s gravitational pull also splits them into two separate jets, meaning that the image produced by the LAT appears as two distinct lights. The separated jets travel at different speeds, meaning they reach the Fermi at different points in time. For B0218+357, the two jets arrive just a third of an arcsecond apart from one another. This is the smallest separation that has yet been recorded.

These two circles represent the visible image of the blazar B0218+357. The presence of two circles indicates the splitting of the gamma rays into two distinct paths upon crossing through the spiral galaxy. The arms of the spiral galaxy are visible on the edges of the gamma rays.

The ability of the Fermi telescope to gather information from B0218+357 could be a huge step forward in understanding distant galaxies and the emission centers of their black holes. Astronomers are also hopeful that the Fermi could eventually be used to locate other gravitational lenses, and thus gain insight on other distant galaxies like B0218+357. Some even suspect that further observations of gravitational lenses could shed new light on major cosmological properties, possibly including constraints to the Hubble constant.

It being a telescope, I’m assuming you can pick up your very own Fermi at your local mall’s Brookstone or order one from whatever SkyMall catalog you find on your next JetBlue flight.